. All the other columns must be "aggregated" by one of <code>SUM</code>,

+

of <code>continent</code>. All the other columns must be "aggregated" by one of <code>SUM</code>,

−

<code>COUNT</code> ...</p>

+

<code>COUNT</code> ...

−

<p>The <code>HAVING</code> clause allows use to filter the groups which are

+

−

displayed. The <code>WHERE</code> clause filters rows before the aggregation,

+

The <code>HAVING</code> clause allows use to filter the groups which are

−

the <code>HAVING</code> clause filters after the aggregation.</p>

+

displayed. The <code>WHERE</code> clause filters rows before the aggregation,

−

<p>If a <code>ORDER BY</code> clause is included we can refer to columns by

+

the <code>HAVING</code> clause filters after the aggregation.

−

their position.</p>

+

+

If a <code>ORDER BY</code> clause is included we can refer to columns by

+

their position.

<div class='qu'>

<div class='qu'>

−

For each region show the number of countries:

+

For each continent show the number of countries:

−

bbc('''name''', region, area, population, gdp)

+

world('''name''', continent, area, population, gdp)

<source lang='sql' class='def'>

<source lang='sql' class='def'>

−

SELECT region, COUNT(name)

+

SELECT continent, COUNT(name)

−

FROM bbc

+

FROM world

−

GROUP BY region

+

GROUP BY continent

</source>

</source>

<source lang='sql' class='ans'>

<source lang='sql' class='ans'>

−

SELECT region, COUNT(name)

+

SELECT continent, COUNT(name)

−

FROM bbc

+

FROM world

−

GROUP BY region

+

GROUP BY continent

</source>

</source>

</div>

</div>

<div class='qu'>

<div class='qu'>

−

For each region show the total population:

+

For each continent show the total population:

−

bbc('''name''', region, area, population, gdp)

+

world('''name''', continent, area, population, gdp)

<source lang='sql' class='def'>

<source lang='sql' class='def'>

−

SELECT region, SUM(population)

+

SELECT continent, SUM(population)

−

FROM bbc

+

FROM world

−

GROUP BY region

+

GROUP BY continent

</source>

</source>

<source lang='sql' class='ans'>

<source lang='sql' class='ans'>

−

SELECT region, SUM(population)

+

SELECT continent, SUM(population)

−

FROM bbc

+

FROM world

−

GROUP BY region

+

GROUP BY continent

</source>

</source>

</div>

</div>

Line 51:

Line 53:

WHERE and GROUP BY

WHERE and GROUP BY

The WHERE filter takes place before the aggregating function.

The WHERE filter takes place before the aggregating function.

−

For each relevant region show the number of countries that has a population

+

For each relevant continent show the number of countries that has a population

of at least 200000000.

of at least 200000000.

<source lang='sql' class='def'>

<source lang='sql' class='def'>

−

SELECT region, COUNT(name)

+

SELECT continent, COUNT(name)

−

FROM bbc

+

FROM world

WHERE population>200000000

WHERE population>200000000

−

GROUP BY region

+

GROUP BY continent

</source>

</source>

<source lang='sql' class='ans'>

<source lang='sql' class='ans'>

−

SELECT region, COUNT(name)

+

SELECT continent, COUNT(name)

−

FROM bbc

+

FROM world

WHERE population>200000000

WHERE population>200000000

−

GROUP BY region

+

GROUP BY continent

</source>

</source>

</div>

</div>

Line 72:

Line 74:

The HAVING clause is tested after the GROUP BY. You can test the aggregated

The HAVING clause is tested after the GROUP BY. You can test the aggregated

values with a HAVING clause.

values with a HAVING clause.

−

Show the total population of those regions with a total population of at

+

Show the total population of those continents with a total population of at

least half a billion.

least half a billion.

<source lang='sql' class='def'>

<source lang='sql' class='def'>

−

SELECT region, SUM(population)

+

SELECT continent, SUM(population)

−

FROM bbc

+

FROM world

−

GROUP BY region

+

GROUP BY continent

HAVING SUM(population)>500000000

HAVING SUM(population)>500000000

</source>

</source>

<source lang='sql' class='ans'>

<source lang='sql' class='ans'>

−

SELECT region, SUM(population)

+

SELECT continent, SUM(population)

−

FROM bbc

+

FROM world

−

GROUP BY region

+

GROUP BY continent

HAVING SUM(population)>500000000

HAVING SUM(population)>500000000

</source>

</source>

Revision as of 23:18, 8 December 2012

World Country Profile

GROUP BY and HAVING

By including a GROUP BY clause functions such as
SUM and COUNT
are applied to groups of items sharing values. When you specify
GROUP BY continent
the result is that you get only one row for each different value
of continent. All the other columns must be "aggregated" by one of SUM,
COUNT ...

The HAVING clause allows use to filter the groups which are
displayed. The WHERE clause filters rows before the aggregation,
the HAVING clause filters after the aggregation.

If a ORDER BY clause is included we can refer to columns by
their position.

For each continent show the number of countries:

world(name, continent, area, population, gdp)

SELECT continent,COUNT(name)FROM world
GROUPBY continent

SELECT continent,COUNT(name)FROM world
GROUPBY continent

For each continent show the total population:

world(name, continent, area, population, gdp)

SELECT continent,SUM(population)FROM world
GROUPBY continent

SELECT continent,SUM(population)FROM world
GROUPBY continent

WHERE and GROUP BY
The WHERE filter takes place before the aggregating function.
For each relevant continent show the number of countries that has a population
of at least 200000000.

SELECT continent,COUNT(name)FROM world
WHERE population>200000000GROUPBY continent

SELECT continent,COUNT(name)FROM world
WHERE population>200000000GROUPBY continent

GROUP BY and HAVING
The HAVING clause is tested after the GROUP BY. You can test the aggregated
values with a HAVING clause.
Show the total population of those continents with a total population of at
least half a billion.